The invention relates to a compressor in an exhaust gas turbocharger for an internal combustion engine wherein the compressor includes a compressor wheel and adjacent the compressor wheel, an auxiliary rotor wheel which is axially movable and can be coupled to the compressor wheel for rotation therewith, and to a method for operating such a compressor.
DE 100 61 847 A1 describes an exhaust gas turbocharger for an internal combustion engine, which exhaust gas turbocharger has an exhaust gas turbine arranged in the exhaust system of the internal combustion engine and has a compressor arranged in the intake tract, with an auxiliary rotor wheel being mounted in the compressor inlet duct upstream of the compressor wheel of the compressor, the auxiliary rotor wheel being separate from, and arranged coaxially with respect to the compressor wheel. The auxiliary rotor wheel is intended to positively influence the operating behavior of the compressor since the surge limit of the compressor is moved in the direction of lower volume flow rates and the choke limit is moved in the direction of higher volume flow rates. The auxiliary rotor wheel, which rotates independently of the compressor wheel, is driven by an electric motor.
It is known from the document DE 100 49 198 A1 to arrange an adjustable blocking element in the inlet duct of a compressor, upstream of the compressor wheel, for variably adjusting the effective cross section of the inlet duct. This design offers the advantage that the cross-section of the compressor inlet duct is variably adjustable, likewise making it possible to manipulate the operating behavior of the compressor. It is for example possible in particular to influence the flow speed and the angular momentum of the supplied combustion air, for example to increase the flow inlet speed of the supplied air by means of a constriction of the cross section. At low loads and speeds, the compressor can be used as an air-driven turbine (so-called cold air turbine mode) utilizing a pressure drop across the compressor to drive the compressor wheel. This pressure drop corresponds to a throttle action in the intake tract, which offers the advantage that the internal combustion engine can be fundamentally operated without a throttle flap. A further advantage is that the charger speed can be kept at a minimum level even at low loads and speeds of the internal combustion engine.
An exhaust gas turbocharger for an internal combustion engine is known from DE 100 50 161 Al, the compressor of which is arranged in the intake tract of the internal combustion engine and is driven by the exhaust gas turbine. A compressor wheel which, when driven, sucks combustion air from the atmosphere and compresses it to an increased charge pressure is rotatably mounted in the compressor inlet duct which is formed in the compressor housing. In order to increase efficiency in particular in low load and speed ranges, it is possible to activate an electric motor comprising a rotor, which rotor is mounted coaxially with respect to the compressor wheel, upstream in the compressor inlet duct, and a stator which is fixed to the housing. Additional combustion air is sucked in by the rotor, which rotates independently of the compressor wheel, when the electric motor is activated. The rotor of the electric motor can also be moved into a coupled position in which it is connected in a positively locking fashion to the compressor wheel, so that the compressor wheel is also driven when the electric motor is activated.
It is the object of the present invention to improve the operating behavior of an exhaust gas turbocharger of an internal combustion engine, in particular for providing a fast charge air pressure build-up during low loads and low engine speeds.